The invention relates to a damped stepping motor for the driving of a measuring mechanism, particularly a roller counting mechanism having a control circuit arrangement which has at least one amplifier as controlled switch.
The invention relates to the above and wherein coils of the stepping motor are fed with approximately square pulses in accordance with measurement pulses supplied by a measurement transmitter.
The prior art includes a mechanical odometer having an electric motor which drives digit wheels by means of a worm/sprocket-wheel transmission. The electric motor may be of the stepping or DC type. The motor is fed with an exciter signal, for instance a series of bipolar pulses indicating the speed of the vehicle. In order to prevent an undesired reversal of the odometer which is connected with the motor as well as a vibrating of the transmission wheels transmitting the rotary energy from the motor to the digit wheels, use is made of a support of the type of a one-way clutch for the mounting of the drive shaft of the electric motor (Federal Republic of Germany OS No. 31 27 141). This one-way clutch, however, results in a substantial increase in the structural expense and is furthermore subject to wear.
Attempts have already been made to damp the noise developed by measuring mechanisms connected to stepping motors, particularly counting mechanisms. The development of noise is particularly disturbing when such measuring mechanisms or counting instruments are used in combination with other, but electronically operating, indicating devices which naturally produce practically no noise. The reason for the development of noise on the part of the measuring mechanisms of counting mechanisms is the intermittent stepping movement of the stepping motor. Its rotor swings beyond the desired position to be reached in each case as a result of its moment of inertia and then back again. As a result, noise is caused by the tooth backlash present between the gear elements--worm and worm wheel. The oscillating movements produced by the stepping motor are transmitted up to the number rollers and counter pinions.
In a series counter forming part of the prior art it has been attempted to reduce the influence of motor oscillations in step-down gearings by a high transmission ratio so that the number rollers and pinions insofar as possible no longer oscillate. This high transmission, however, results in greater expense than a smaller transmission ratio.
One could consider reducing the noise by the use of relative soft materials for the transmission elements such as worm and worm wheel as well as drive sprockets. The manufacture of these parts from soft materials which are to be connected to other materials at particular places is, however, expensive. Furthermore, such measures are frequently still not sufficient in order to obtain the desired quiet operation.
Furthermore, mechanical damping devices can be provided, particularly ones operating on the frictional-force principle, but the usable motor torque is weakened by this damping measure and the operating limits of the motor are reduced. For at least partial compensation the starting voltage or the amplitude of the pulses feeding the motor must be increased. The possibility of using friction-dampening means is thereby limited.
Other mechanical damping-devices can also be used only to a limited extent and with difficulty since, as a rule, they require additional space and/or increase the expense of construction or operation for the combination of the stepping motor with the measuring mechanism.
Oil-damping-systems, possibly in combination with epilamization, have the disadvantage that the degree of damping depends essentially on the amount of oil and its viscosity. In case of escaping oil, reductions in damping or possibly disturbances in operation are to be feared.
In accordance with another principle, the rotor of the stepping motor can be connected via a spring storage device to the transmission elements--worm or worm wheel. Such a spring storage device can, however, be designed only optimally for one frequency while for the drive of measuring mechanisms the stepping motor is customarily acted on by a large difference in frequencies, for instance from 0 to 4 Hertz.
It is thus an object of the present invention to develop a damped stepping motor having a control circuit arrangement in such a manner that an effective damping of noise is obtained with the same amplitude of exciter pulse and stepping frequency without reducing the reliability of operation.
In this connection the fundamental disadvantages of mechanical damping devices such as large stepping-up of the transmission coupling the stepping motor with the measuring mechanism, use of relatively soft materials for gear elements, friction damping, oil dampers or spring storages are to be avoided. It is important that, even when employing the dampening in accordance with the invention, a large frequency range of the measurement pulses be conducted without error to the measuring mechanism.